1. Field of the Invention
The present invention relates to a pump comprising a rotor made of synthetic resin and a housing for the rotor arranged adjacent to the rotor with a gap formed between the housing and the rotor to raise the pressure of a medium obtained by adding water to a solution, and further to a medium circulation apparatus using the pump.
2. Description of the Related Art
In the case of the above pump, the rotor is made of synthetic resin to decrease its weight, for example. However, if moisture is contained in a medium, the rotor made of synthetic resin is swelled by the moisture contained in the medium, the gap dimension between the housing and the rotor changes whereby the desired pump performance may not be obtained. Therefore, it is if necessary to control the swelling of the rotor. Thus, Japanese Patent application Laid-Open No. 3-115794 discloses a material for suppressing the swelling of a rotor made of synthetic resin. In order to suppress the swelling due to the moisture contained in fuel, the rotor is made of a material obtained by blending phenol aralkyl resin and a filler with phenol resin.
However, the above conventional rotor is used for a pump for force-feeding a fuel having a moisture content rate of up to approx. 0.5 wt %. In the case of a medium containing a solution that causes corroding of a light metal, Japanese Patent Publication No. 63-12504 discloses that corrosion resistance can be provided for the light metal by adding water to the solution until the moisture content rate of the medium is up to about 15 wt %. However, when applying the pump disclosed in Japanese Patent application Laid-Open No. 3-115794 to the medium having a large moisture content rate as mentioned above, there is insufficient swelling resistance and the desired pump performance cannot be obtained.
Therefore, it is desired that a sufficient pump performance be obtained even when force-feeding a medium having a relatively large moisture content rate by a pump using a rotor made of synthetic resin. In the case of this pump, however, the gap dimension between the rotor and the housing greatly influences the pump performance. Therefore, in order to obtain a sufficient pump performance, it is necessary to secure a minimum gap dimension. Then, based on the minimum gap dimension, it is possible to set the upper limit value of the dimensional change rate of a rotor due to the swelling. On the other hand, in order to improve the corrosion resistance of a light metal, it is indispensable to set the degree of freedom of the moisture content rate of the medium, that is, the increased range of water quantity to be added, at a relatively large value and it is necessary to select synthetic resin for forming a rotor so that the degree of freedom of the moisture content rate in the medium can be relatively large with respect to the upper-limit dimensional change rate of the rotor due to the above-described swelling.